1. Field of the Invention
The present invention relates to a three-dimensional printing apparatus.
2. Description of the Related Art
A three-dimensional printing apparatus for forming a three-dimensional object is conventionally known (for example, see JP 2003-39564 A). The three-dimensional printing apparatus applies light to a liquid photocurable resin accommodated in a vat to cause the photocurable resin to cure, so as to form a three-dimensional object.
This type of three-dimensional printing apparatus forms a three-dimensional object by preparing cross-sectional shapes of the three-dimensional object and successively stacking resin layers each being formed by curing a photocurable resin and having a shape corresponding to one of the cross-sectional shapes. For example, the three dimensional printing apparatus has a platform having an opening formed therein, a vat placed on the platform and made of a resin, for accommodating a photocurable resin, and a holder being disposed above the vat and capable of being raised and lowered. An optical system is disposed below the platform. The optical system includes a light source for emitting light, a mirror, and so forth. The light emitted from the light source is reflected by the mirror. The light reflected by the mirror is applied to the photocurable resin in the vat through the opening of the platform. A portion of the photocurable resin in the vat that is exposed to the light is cured.
The exposed position that is exposed by the light applied from the light source is controlled according to the cross-sectional shape, whereby the position of the resin to be cured is changed as desired. This enables the cured resin to form the cross-sectional shape. Then, the holder is elevated step by step, so that the desired cross-sectional shape is consecutively formed toward the bottom. In this way, the desired three-dimensional object is formed.
When three-dimensional objects are formed using the same vat for a long period of time, the part of the vat that has been exposed to light may often become opaque (this phenomenon is hereinafter referred to as “whitening”). When light is applied to the whitened vat to cure the photocurable resin inside the vat, part of the light is blocked by the whitened portion of the vat. Consequently, the photocurable resin may not be cured appropriately in an adjacent region to the whitened portion of the vat. This may prevent formation of a desired cross-sectional shape. As a consequence, the product quality of the resulting object may be degraded.